Aircraft are shrouded in haze at Kuala Lumpur International Airport in Malaysia on March 14. / Charles Pertwee, Bloomberg

by Bart Jansen, USA TODAY

by Bart Jansen, USA TODAY

While passenger jets have several chatty pieces of technology that relay information in flight, the relative silence from Malaysia Airlines Flight 370 makes it harder to find the jet and deepens the mystery about what happened to it.

The airline insists the last automated information from the jet's maintenance system came at 1:07 a.m. Saturday. FlightRadar24, a flight-tracking system that followed the jet in the Gulf of Thailand, got its last signal from the jet's transponder at 1:21 a.m.

The fact that the two pieces of equipment stopped signaling at different times doesn't necessarily suggest foul play, pilots and tracking experts said.

"There could have been some cascading series of malfunctions and failures caused by something bizarre," said Patrick Smith, a commercial pilot who writes the blog askthepilot.com. "It really could go either way â?? foul play or some sort of catastrophic malfunction. You just don't know."

One way to track an airliner is through its transponder, which includes a transmitter and responder. The equipment, which planes carry with two channels in case one fails, relays information with a four-digit code that identifies the plane. The system helps air-traffic controllers track planes and helps planes avoid colliding with each other.

The version of the equipment aboard Malaysia's 777 sent information about the jet's altitude, latitude, longitude and heading.

FlightRadar24 got two signals per minute from the jet's transponder during the final 10 minutes that the Malaysia flight was tracked at 35,000 feet above the Gulf of Thailand en route from Kuala Lumpur to Beijing.

Two minutes before the final signal, the heading changed 15 degrees. The jet's flight plan called for the adjustment on March 4 and 8, according to FlightRadar24.

Despite media reports that the jet turned from heading northeast to the west, FlightRadar24 said Friday it "has not tracked this."

The lack of signal is why some aviation experts feared the jet crashed at that point. The search focused on that area for the first five days â?? without finding any wreckage.

Fredrik Lindahl, CEO of FlightRadar24, said the company hadn't received any distress signals from the jet before losing track of it. Reasons for being unable to track the jet include the transponder being turned off, the transponder malfunctioning or having the aircraft drop below 30,000 feet, he said.

FlightRadar24 can't track planes flying lower than 30,000 feet in that area because its coverage is shaped like a funnel from the antenna receiver, with high altitude covered farther than low altitude, Lindahl said.

Smith said transponders occasionally malfunction or send out incorrect data, but pilots are able to turn them on and off to get them working again.

"Air-traffic control will often ask you to 'cycle' your transponder â?? turn it off and back on," Smith said. "A transponder has different modes that are responsible for different data. It's not just on/off."

Possibilities for the lack of signal include the pilot turning off the equipment, either with a switch or with a circuit-breaker; an electrical fire that could knock out different pieces of equipment; or a catastrophe that broke the jet apart.

"There are all kinds of possibilities," said Capt. Sean Cassidy, first vice president and national safety coordinator for the Air Line Pilots Association, a union with 50,000 members. "You could have had some kind of emergency situation on the plane."

The search widened to the Indian Ocean because of another piece of technology aboard the jet, which relayed maintenance information to the airline.

Despite being turned off or becoming disabled at 1:07, the equipment called ACARS, for Aircraft Communications Addressing and Reporting System, kept trying to contact a satellite for four hours after people on the ground lost contact with the jet. The additional flying time meant the jet could have gone thousands of miles from where it was last tracked.

Besides Indian ships and planes, the USS Kidd is moving to the western search area in the Indian Ocean at the request of the Malaysian government, said Army Col. Steve Warren, a Pentagon spokesman. In addition, a Navy P-8 surveillance jet will search the Indian Ocean on the Bay of Bengal.